1. Field of the Invention
The present invention relates to a method for producing a support for planographic printing plates, to a support for planographic printing plates, and to a planographic printing plate precursor. In particular, the invention relates to a method for producing a support for planographic printing plates, in which aluminum plates produced from regenerated aluminum ingots such as those from scrapped and recycled aluminum can be used for the material; to a support for planographic printing plates, which is produced according to the method; and to a planographic printing plate precursor, which is fabricated by forming a thermosensitive or photosensitive plate layer on the surface of the support for planographic printing plates.
The invention also relates to an aluminum plate for planographic printing plate supports, which is used as the material in the above-mentioned production method; to a planographic printing plate support formed from the aluminum plate; and to a method for inspecting aluminum plates for planographic printing plate supports. In particular, the invention relates to an aluminum plate for planographic printing plate supports, which is inexpensive and which, when processed into planographic printing plate precursors in a sequential process of roughening its surface followed by forming a plate layer thereon, is almost free from the trouble of feed disorder such as meandering, and which is therefore favorable to the production of planographic printing plate precursors; to a planographic printing plate support formed from the aluminum plate; and to a method for inspecting aluminum plates for planographic printing plate supports, in which a roll of a rolled aluminum plate fed into a device to be processed into planographic printing plate supports is inspected as to whether or not it is likely to encounter the feed disorder as described above by the use of a simple tool in a simplified manner.
2. Description of the Related Art
In general, a planographic printing plate precursor is fabricated in a process that comprises roughening the surface of a pure aluminum or aluminum alloy plate (this is hereinafter referred to as xe2x80x9caluminum platexe2x80x9d), then subjecting the surface thereof to anodic oxidation to thereby form an oxide film thereon to give a planographic printing plate support, and applying a photosensitive or thermosensitive resin onto the surface of the oxide film formed on the planographic printing plate support to thereby form a photosensitive or thermosensitive plate layer thereon. The photosensitive resin layer and the thermosensitive resin layer that are optionally combined with an undercoat layer and a protective layer are known, for example, in JP-A 62333/2000, 101651/1984 and 149491/1985.
Images including letters and pictures are printed on the plate layer of the planographic printing plate precursor, and they are developed thereon to complete a planographic printing plate.
For roughening the surface of an aluminum plate, for example, the plate surface is mechanically processed with a brush roller having nylon hair or the like or with a roughening roller of which the surface is made of an abrasive cloth (mechanical surface roughening); or chemically processed in an alkaline solution (etching); or electrolytically processed in an acidic electrolyte (electrolytic solution) by applying an alternating current to the aluminum plate serving as one electrode therein (AC electrolysis).
For ensuring good water balance in printing, in general, the plate surface is first mechanically roughened, then etched and electrolytically roughened.
After the step of electrolytic surface roughening and the step of chemical surface roughening thereof, the aluminum plate may be optionally desmutted by dipping it in an acid solution to thereby remove oxides, hydroxides and intermetallic compounds of the elements that may be deposited in the aluminum plate as a result of the process of electrolytic surface roughening and chemical surface roughening.
Regenerated aluminum ingots such as those from scrapped and recycled aluminum are more inexpensive than virgin ones, and the energy consumption at the time of production thereof is relatively small. Therefore, producing planographic printing plate precursors from aluminum plates that are prepared from such regenerated aluminum ingots is favorable in point of cost and energy saving and even in point of natural resource saving.
Different from virgin ones, however, adequate control on the alloy components is hardly done for regenerated aluminum ingots (that is, their aluminum purity is no higher than 97% by weight) and the aluminum ingots contain various impurities.
Therefore, various intermetallic compounds and deposits that result from the impurities are exposed out on the surface of the aluminum plates produced from such regenerated aluminum ingots, and the planographic printing plate precursors formed from these aluminum plates often involve defects in the oxide film thereof formed through anodic oxidation. The defects often cause serious ink stains in which ink is attached spotwise on the entire surface of printed matters.
Another problem with aluminum plates that contain many impurities, such as those produced from regenerated aluminum ingots, is that their surfaces are difficult to evenly roughen in an electrochemical process, and, when electrochemically processed, their surfaces are unevenly roughened. Therefore, when such aluminum plates are used in fabricating printing plates and when the thus-fabricated printing plates are used in printing units, ink tends to adhere to and stain the blanket of offset rollers (blanket staining), and then it is transferred onto printed papers to stain them.
In the electrolytic surface-roughening step in the process of producing planographic printing plate supports, used is an alternating current or a direct current. In particular, in case where an alternating current is used in the step, the profile of the roughened surface of the supports often varies greatly, depending on the waveform of the current employed, and when the composition of the aluminum material for the supports is varied, it is often difficult to keep the intended profile of the roughened surface of the supports in a predetermined range. This is one problem with the electrolytic surface-roughing process, and to solve it, the waveform of the current to be employed in the process must be strictly controlled.
In addition, when planographic printing plate precursors are produced from recycled aluminum, scrapped aluminum, and regenerated ingots such as those mentioned above, the mechanical properties thereof greatly vary. When such planographic printing plate precursors are exposed to light, developed and processed into printing plates by the use of an automatic photomechanical device, and when the resulting planographic printing plate is set around the blanket in a planographic offset printer, the planographic printing plate may be involved with various problems. Concretely, the printing plate set in a printer often causes paper feeding disorder such as paper entangling or meandering, and it is often lifted up from the blanket and cannot be well fitted thereto.
Aluminum webs are produced by hot-rolling a cast slab of aluminum and then cold-rolling it to have a predetermined thickness. In general, they are stored and delivered in the form of rolls, after coiled up around roll cores.
In general, aluminum ingots are so rolled into webs that the center part of the resulting webs is thicker than the edges thereof. This is in order that the edges of the aluminum web wound up in coils are prevented from being deformed when roughly contacted with each other.
However, when aluminum ingots are so rolled into webs that the center part of the resulting webs is thicker than the edges thereof, the edges are elongated larger than the center part, and, as a result, the edges are often waved or slacked in the wavy manner (which wavy deformation at the edge portions will be referred to as the xe2x80x9cedge strainxe2x80x9d hereinafter). If the edge strain is great, it causes feed disorder when the aluminum webs are processed into planographic printing plate precursors. In addition, the edge strain causes paper travel disorder when the resulting planographic printing plate precursors are further processed into printing plates, and fitting failure onto the blanket when the printing plate is set in an offset printer.
In case where virgin ingots, mother alloys and pure metal additives are used in preparing cast slabs, the substantially the same rolling characteristics can constantly be achieved in the obtained cast slabs. Accordingly, the edge strain can be relatively easily controlled within a predetermined range by adjusting the rolling condition.
However, recycled aluminum, scrapped aluminum and regenerated aluminum ingots generally have low aluminum purity and adequate control on the alloy components thereof has hardly been done, as described above. Therefore, the rolling characteristics of the cast slabs produced from these recycled aluminum, scrapped aluminum and regenerated ingots vary significantly. As a result, when such cast slabs are rolled into aluminum webs, it is often difficult to control their edge strain to fall within a predetermined range by simply adjusting the rolling condition.
For these reasons, it has heretofore been said that practicable planographic printing plates cannot be produced from regenerated aluminum ingots.
The invention is to solve the above-mentioned problems, and its objects are to provide an aluminum plate for planographic printing plate supports, which can be produced from recycled aluminum, scrapped aluminum and regenerated aluminum ingots as those mentioned above and which, when formed into printing plates, free from the troubles of feed disorder and fitting disorder to blankets; to provide a planographic printing plate precursor in which the aluminum plate is used for the support; and to provide a method for inspecting aluminum plates for planographic printing plate supports, in which a roll of a rolled aluminum plate fed into a device to be processed into planographic printing plate supports is inspected as to whether or not it is likely to encounter the aforementioned feed disorder and the fitting disorder to blankets, by using a simple tool in a simplified manner.
To solve the above-mentioned problems, the principal objects of the present invention are to provide a method for producing a support for planographic printing plates, in which a support (for planographic printing plates), which results in planographic printing plates of good printing durability that do not cause serious ink stains on printed matters and do not cause blanket staining, can be produced even when aluminum plates prepared from regenerated aluminum ingots which have been subjected to no alloy control are used; to provide a support for planographic printing plates obtained in the method; and to provide a planographic printing plate precursor comprising the support.
Other objects of the invention are to provide an aluminum plate for lithographic printing plate supports, which can be produced even from recycled aluminum, scrapped aluminum and regenerated ingots such as those mentioned above and which, when formed into printing plates, free from the troubles of feed disorder and fitting disorder to blankets; to provide a lithographic printing plate precursor for which the aluminum plate is used as the support; and to provide a method for inspecting aluminum plates for lithographic printing plate supports, in which a roll of a rolled aluminum plate fed into a device to be processed into planographic printing plate supports is inspected as to whether or not the aluminum plate is likely to encounter the feed disorder and the fitting disorder to blankets as above, by the use of a simple tool in a simplified manner.
The first aspect of the invention is a method for producing a support for planographic printing plates, which comprises a step of roughening at least one surface of an aluminum plate and in which the surface-roughening step includes (a) a pre-electrolytic surface-roughening step of electrolytically pre-roughening the surface of the aluminum plate in an aqueous hydrochloric acid solution that contains hydrochloric acid as the essential acid ingredient, (b) an alkali-etching step of contacting the aluminum plate of which surface has been electrolytically pre-roughened in the previous pre-electrolytic surface-roughening step, with an alkali solution to etch it, (c) a desmutting step of desmutting the aluminum plate having been etched in the previous alkali-etching step, with sulfuric acid by contacting the aluminum plate with an aqueous sulfuric acid solution having a sulfuric acid concentration of from 250 to 500 g/liter and an aluminum ion concentration of from 1 to 15 g/liter and having a liquid temperature falling between 60 and 90xc2x0 C., for a contact period of time falling between 1 and 180 seconds, and (d) an electrolytic surface-roughening step of processing the aluminum plate having been desmutted in the previous desmutting step, in an aqueous nitric acid solution with an alternating current being applied thereto.
In the desmutting step in this aspect, the aluminum plate is processed with sulfuric acid having a predetermined aluminum concentration, to thereby remove the intermetallic compounds and a simple substance Si that exist on the surface of the aluminum plate and cause uneven electrolytic surface-roughening treatment to form uneven honeycomb pits in the roughened surface. The honeycomb pits referred to herein are meant to indicate that micropores formed in the roughened surface are closely adjacent to each other to thereby make the roughened surface have a honeycomb-like appearance.
Therefore, even when aluminum plates prepared from regenerated aluminum ingots that contain a relatively large amount of silicon and manganese which may form intermetallic compounds and a simple substance Si are used in the method, the surfaces of the aluminum plates are well uniformly processed in the electrolytic surface-roughening step that follows the desmutting step with sulfuric acid, and uniform honeycomb pits are formed in their surfaces. Accordingly, the support produced in the method is favorable to planographic printing plates.
Before processed in the electrolytic surface-roughening step, the surface of the aluminum plate is electrolytically pre-roughened in an aqueous hydrochloric acid solution in the pre-roughening step of processing it. Therefore, the support for planographic printing plates produced in the method is uniformly processed and is free from streaks in its surface.
In the second aspect of the invention, the surface-roughening step includes an etching step, prior to the pre-electrolytic surface-roughening step, of contacting the aluminum plate with an alkali solution to etch the aluminum plate (which etching step will be referred to as xe2x80x9cthe etching step prior to the pre-electrolysisxe2x80x9d hereinafter).
In the present aspect, the pre-electrolytic surface-roughening step is effected after the etching step prior to the pre-electrolysis. In the etching step prior to the pre-electrolysis, the surface of the aluminum plate dissolves in an alkali solution, and, in particular, the area of hillocks that protrude greatly from the area around them at the surface of the aluminum plate dissolves first in the solution. Therefore, even when the surface of the aluminum plate has large hillocks, recesses and other defects, such projection/recesses are smoothed well in the etching step prior to the pre-electrolytic surface-roughening step.
In the present aspect, it is desirable that the aluminum plate is, after etched but before pre-electrolyzed, desmutted in an aqueous acid solution, so that the oxides, hydroxides and intermetallic compounds of the impurity elements having formed on the etched surface of the aluminum plate can be removed by the desmutting treatment.
In the third aspect of the invention, the surface-roughening step includes a mechanical surface-roughening step of mechanically roughening at least one surface of the aluminum plate, prior to the pre-electrolytic surface-roughening step.
In the present aspect, the mechanical surface-roughening treatment in the step produces uniform and non-directional grains in the roughened surface of the aluminum plate. In this, therefore, the surface of the aluminum plate roughened in the surface-roughening step has good water retentiveness. Accordingly, the support for planographic printing plates obtained according to the production method ensures good water-ink balance of planographic printing plates.
In the fourth aspect of the invention, the surface roughening step includes: an etching step of etching the aluminum plate, of which surface has been roughened in the electrolytic surface-roughening step, with an alkali solution (which etching step will be referred to as xe2x80x9cthe etching step after the electrolysisxe2x80x9d hereinafter); and a final desmutting step of desmutting the aluminum plate which has been etched in the etching step after the electrolysis, by contacting the aluminum plate with an aqueous sulfuric acid solution.
In the electrolytic surface-roughening step, the aluminum plate is electrolyzed with an alternating current applied thereto. In this, therefore, a minus voltage and a plus voltage in periodic cycles are alternately applied to the aluminum plate. While having received a minus voltage, the aluminum plate undergoes anodic reaction, and its surface is thereby dissolved to have honeycomb pits formed therein. On the other hand, while having received a plus voltage, the aluminum plate undergoes cathodic reaction to thereby have an aluminum hydroxide film formed thereon.
The aluminum hydroxide film formed on the surface of the aluminum plate through such cathodic reaction is dissolved and removed in the etching step after the electrolysis in which the aluminum plate is processed with an alkali solution.
The smut formed on the surface of the aluminum plate in the etching step after the electrolysis is removed in the final desmutting step.
Accordingly, the aluminum plate of which surface has been roughened in the surface-roughening step of the present invention well receives an anodic oxide film thereon. In other words, in the aluminum plate of the present invention, an anodic oxide film can be evenly formed on the aluminum plate through anodic oxidation.
In the fifth aspect of the invention, the aluminum plate is etched, in the etching step after the electrolysis, so that 0.01 to 5 g/m2 of the surface of the aluminum plate is dissolved.
In the present aspect, the etching step after the electrolysis is so controlled that the fine hillocks and recesses of the surface of the aluminum plate formed in the electrolytic surface-roughening step may remain after the step in an appropriate manner. A planographic printing plate precursor which is less likely to cause blanket staining or serious ink stains on printed papers can be produced from the support for planographic printing plates obtained in the present aspect.
In the sixth aspect of the invention, the aluminum plate is etched, in the etching step prior to the pre-electrolytic surface-roughening step, 1 to 15 g/m2 of the aluminum plate is dissolved.
To fabricate a planographic printing plate precursor, a plate layer is formed on the roughened surface of the support obtained in the production method of the present aspect. The advantage of the thus-fabricated printing plate precursor is that it is free from the problem of serious ink staining on printed matters and from the problem of blanket staining.
In the seventh aspect of the present invention, in the electrolytically surface-roughening step, an AC electrolytic cell having therein a counter electrode to impart an alternating current to the aluminum plate is used, and the alternating current to be applied thereto is so controlled that the quiescent time for which no current flows between the aluminum plate and the counter electrode falls between 0.001 and 0.6 second and that the pulse rise time, Tp, within which the current waveform rises up falls between 0.01 and 0.3 millisecond.
According to this aspect, uniform honeycomb pits are formed at the surface of the aluminum plate processed in the electrolytic surface-roughening step. That is, the support for planographic printing plates obtained in this production method is excellently good, as its surface is uniformly roughened.
When two or more electrolytic cells of the type are used for the electrolytic treatment, no current flows between the aluminum plate and the counter electrode in one electrolytic cell and also between the aluminum plate and the counter electrode in any of the other electrolytic cells while the aluminum plate having been processed in that one electrolytic cell is taken out of it and then introduced into the next one electrolytic cell adjacent to the first one cell. In this case, therefore, it is desirable that the electrolytic cells are so disposed that the time for which the aluminum plate is between the first one cell and the next one cell, not being put in both of them, falls 0.001 and 0.6 seconds.
In the eighth aspect of the invention, the production method includes a step of anodic oxidation to form an oxide film on the surface of the aluminum plate of which the surface has been roughened in the surface-roughening step.
In this aspect, the roughened surface of the aluminum plate is coated with a hard and dense oxide film formed through anodic oxidation. Therefore, the support produced in the production method realizes planographic printing plates of good durability.
In the ninth aspect of the invention, the anodic oxidation step includes a step of hydrophilicating the oxide film formed on the surface of the aluminum plate.
The advantage of the support for planographic printing plates produced according to the production method of this aspect is that the adhesiveness between the oxide film and the plate layer to be formed thereon is good.
In the tenth aspect of the invention, the anodic oxidation step includes a step of sealing micropores that exist in the oxide film formed on the surface of the aluminum plate.
In the support for planographic printing plates produced according to the production method of this aspect, the surface defects in the oxide film are significantly reduced. To fabricate a planographic printing plate precursor, a plate layer is formed on the roughened surface of the support, and the advantage of the thus-fabricated printing plate precursor is that it is free from the problem of serious ink staining on printed matters and from the problem of blanket staining.
In the eleventh aspect of the invention, the aluminum plate has an aluminum content falling between 95 and 99.4% by weight and a silicon content falling between 0.15 and 1% by weight.
In general, regenerated aluminum ingots contain much Si or much Mn.
The production method for planographic printing plate supports of this aspect is one embodiment of applying the invention to aluminum plates prepared from Si-rich regenerated aluminum ingots.
In the twelfth aspect of the invention, the aluminum plate has an aluminum content falling between 95 and 99.4% by weight and a manganese content falling between 0.1 and 1.5% by weight.
The production method for planographic printing plate supports of this aspect is one embodiment of applying the invention to aluminum plates prepared from Mn-rich regenerated aluminum ingots.
The thirteenth aspect of the invention is the support for planographic printing plates produced according to any one of the above-mentioned 1st to 12th aspects.
On the roughened surface of the support of this aspect, formed is a photosensitive or thermosensitive plate layer to fabricate a planographic printing plate precursor. The precursor is processed into a printing plate, and the resulting printing plate is free from the problem of serious ink stains on printed matters and from the problem of blanket staining.
The fourteenth aspect of the invention is a planographic printing plate precursor that comprises the support of the 13th aspect and a photosensitive or thermosensitive plate layer formed on the roughened surface of the support.
The advantage of the planographic printing plate precursor of this aspect is that it realizes a printing plate not causing serious ink stains on printed papers and not causing blanket staining.
The fifteenth aspect of the invention is a method for producing a support for planographic printing plates, which comprises a step of roughening at least one surface of an aluminum plate and in which the surface-roughening step includes an AC-electrolytic surface-roughening step of processing the aluminum plate in an aqueous nitric acid solution having a nitrate ion concentration and an aluminum ion concentration of from 5 to 15 g/liter each, and an ammonium ion concentration of from 10 to 300 ppm, and having a bath temperature falling between 50 and 80xc2x0 C.
In this method, even when the aluminum plate to be processed is prepared from regenerated aluminum ingots such as those mentioned above, its surface can be well roughened through the AC electrolysis of which the condition is specifically defined herein. In the thus-roughened surface, micropores are densely dispersed, and honeycomb pits are uniformly formed to present a honeycomb-like appearance. To fabricate a planographic printing plate, a plate layer is formed on the roughened surface of the support, and the advantage of the thus-fabricated printing plate is that it is free from the problem of serious ink staining on printed matters and from the problem of blanket staining.
In the sixteenth aspect of the invention, the AC-electrolytic surface-roughening step is so controlled that the ratio of the quantity of electricity QA of the alternating current applied to the aluminum plate acting as an anode, to the quantity of electricity QC thereof applied to the aluminum plate acting as a cathode, QA/QC falls between 0.9 and 1, the current duty is 0.5 and the current frequency falls between 40 and 120 Hz.
In this aspect, the aluminum plate is processed to have more uniform honeycomb pits formed therein.
In the seventeenth aspect of the invention, the alternating current to be applied to the aluminum plate in the AC-electrolytic surface-roughening step is so controlled that the pulse rise time, Tp, within which the current waveform rises up falls between 0.01 and 0.3 millisecond, and the quiescent time for which no current flows through the aluminum plate falls between 0.001 and 0.6 second.
As having the advantage of uniform honeycomb pits formed in its roughened surface, the support produced in the production method of this aspect is especially favorable for planographic printing plates.
In the AC-electrolytic surface-roughening step in the eighteenth aspect of the invention, used is an AC electrolytic cell unit which comprises an electrolytic cell containing therein the aqueous nitric acid solution and enabling the aluminum plate to pass through it, a power source for applying an alternating current to the aluminum plate, and a counter electrode disposed inside the cell so as to face the aluminum plate while the plate is electrolytically processed therein, and in which an alternating current is applied between the aluminum plate and the counter electrode to thereby electrolytically roughen the surface of the aluminum plate, and the AC mode is so controlled that it includes at least once the quiescent time for which no alternating current flows between the aluminum plate and the counter electrode and that the quiescent time falls between 0.001 and 0.6 second/once.
When two or more electrolytic cells of the type are connected in series and used for the electrolytic treatment herein, they are preferably so disposed that the time, for which no current flows between the aluminum plate not in any cell and the counter electrode in any one cell while the aluminum plate having been led out of one cell does not as yet reach the next cell, is at longest 0.6 second.
As having the advantage of uniform honeycomb pits formed in its roughened surface, the support produced in the production method of this aspect is especially favorable for planographic printing plates.
In the nineteenth aspect of the invention, the surface-roughening step comprises a first etching step of contacting the aluminum plate with an aqueous alkali solution to etch it, the AC-electrolytic surface-roughening step of roughening the thus-etched surface of the aluminum plate, and a second etching step of further contacting the thus-roughened aluminum plate with an aqueous alkali solution to etch it, in that order.
In this aspect, the aluminum plate is etched before and after its surface is roughened in the AC-electrolytic surface-roughening step. A plate layer is formed on the roughened surface of the support to prepare a planographic printing plate precursor, and the advantage of the precursor is that the image reproducibility of the resulting planographic printing plate is excellent.
In the twentieth aspect of the invention, the aluminum plate is dissolved to a degree of from 1 to 15 g/m2 in the first etching step, and is dissolved to a degree of from 0.01 to 5 g/m2 in the second etching step.
A plate layer is formed on the roughened surface of the support produced in this aspect, to thereby prepare a planographic printing plate precursor. The advantage of the thus-prepared precursor is that the image reproducibility in processing the plate layer therein to complete a planographic printing plate is extremely good.
In the twenty-first aspect of the invention, the surface-roughening step includes a first desmutting step of contacting the aluminum plate with an aqueous acid solution between the first etching step and the AC-electrolytic surface-roughening step, and includes a second desmutting step of further contacting the aluminum plate with an aqueous acid solution after the second-etching step.
In this aspect, the aluminum plate is processed in the first desmutting step prior to the AC-electrolytic surface-roughening step, whereby the intermetallic compounds and a simple substance silicon having deposited on the surface of the aluminum plate are removed. Accordingly, in the next AC-electrolytic surface-roughening step that follows the first desmutting step, the aluminum plate is effectively prevented from being unevenly processed owing to the intermetallic compound and the simple substance silicon, and, as a result, the support for planographic printing plates produced in this aspect has especially uniform honeycomb pits formed on its surface.
In addition, in this aspect, the aluminum plate is, after subjected to the second etching treatment, again desmutted in the second desmutting step, whereby the intermetallic compounds and the simple substance silicone not removed in the first desmutting step and still remaining on the surface of the aluminum plate are completely removed.
Therefore, when a plate layer is formed on the roughened surface of the support produced in this aspect, the resulting planographic printing plate precursor realizes a good printing plate not causing serious ink staining on printed matters and not causing blanket staining.
In the twenty-second aspect of the invention, the surface-roughening step includes a step of mechanically roughening at least one surface of the aluminum plate, prior to the first etching step.
Concretely, in the method of this aspect for producing a support for planographic printing plates, the aluminum plate to be the support is first processed in the mechanical surface-roughening step, then in the first etching step, then in the AC-electrolytic surface-roughening step, and then in the second etching step in that order. Accordingly, the support thus produced in the production method ensures good water-ink balance of planographic printing plates comprising it.
In the twenty-third aspect of the invention, the aluminum plate of which at least one surface has been roughened in the surface-roughening step is subjected to anodic oxidation to thereby form an oxide film on its roughened surface.
The oxide film thus formed on the roughened surface of the aluminum plate is dense and hard. Therefore, the advantage of the support for planographic printing plates produced in the production method of this aspect is that the durability of the roughened surface of the aluminum plate for the support is good.
In the twenty-fourth aspect of the invention, the surface of the aluminum plate having the oxide film formed thereon is made hydrophilic.
The advantage of the support for planographic printing plates produced in the production method of this aspect is that the adhesiveness between the oxide film formed on the roughened surface of the aluminum plate for the support and a plate layer to be formed on the oxide film is good.
In the twenty-fifth aspect of the invention, the anodic oxidation step includes a step of sealing micropores that exist in the oxide film formed on the surface of the aluminum plate.
In the support for planographic printing plates produced according to the production method of this aspect, the surface defects in the oxide film are significantly reduced. To fabricate a planographic printing plate, a plate layer is formed on the roughened surface of the support, and the advantage of the thus-fabricated printing plate is that it is free from the problem of serious ink staining on printed matters and from the problem of blanket staining.
In the twenty-sixth aspect of the invention, the aluminum plate has an aluminum content falling between 95 and 99.4% by weight and a silicon content falling between 0.15 and 1% by weight.
In general, regenerated aluminum ingots contain much Si or much Mn.
The production method for planographic printing plate supports of this aspect is one embodiment of applying the invention to aluminum plates prepared from Si-rich regenerated aluminum ingots.
In the twenty-seventh aspect of the invention, the aluminum plate has an aluminum content falling between 95 and 99.4% by weight and a manganese content falling between 0.1 and 1.5% by weight.
The production method for planographic printing plate supports of this aspect is one embodiment of applying the invention to aluminum plates prepared from Mn-rich regenerated aluminum ingots.
The twenty-eighth aspect of the invention is the support for planographic printing plates produced in the production method of any one of the 15th to 27th aspects mentioned hereinabove.
The twenty-ninth aspect of the invention is a planographic printing plate precursor fabricated by forming a photosensitive or thermosensitive plate layer on the roughened surface of the support of the 28th aspect as above.
The advantage of the planographic printing plate precursor of this aspect, which is fabricated by forming a photosensitive or thermosensitive plate layer on the roughened surface of the support of the 28th aspect as above, is that it realizes a printing plate not causing serious ink stains on printed papers and not causing blanket staining.
The thirtieth aspect of the invention is a method for producing a support for planographic printing plates, which comprises a surface-roughening step of electrolytically roughening an aluminum alloy plate in an acid solution with an alternating current applied thereto, and a step of processing the plate for anodic oxidation, and in which the electrolytic surface-roughening step includes a step of using an AC waveform that takes a pulse rise time falling between 1.5 and 6 milliseconds before it rises from its base (0) to its peak.
In the thirty-first aspect of the invention, the aluminum purity of the aluminum alloy plate falls between 95 and 99.4% by weight.
In the thirty-second aspect of the invention, the aluminum alloy plate contains at least five metals of the following:
Fe: from 0.3 to 1.0% by weight,
Si: from 0.15 to 1.0% by weight,
Cu: from 0.1 to 1.0% by weight,
Mg: from 0.1 to 1.5% by weight,
Mn: from 0.1 to 1.5% by weight,
Zn: from 0.1 to 0.5% by weight,
Cr: from 0.01 to 0.1% by weight, and
Ti: from 0.03 to 0.5% by weight.
In the thirty-third aspect of the invention, the production method of the 30th aspect includes the following steps, before and/or the electrolytic surface-roughening step:
(1) an alkali-etching step of processing the aluminum alloy plate in an aqueous alkali solution to etch it to a degree falling between 1 and 15 g/m2;
(2) a desmutting step of desmutting the alkali-etched aluminum alloy plate in an acid solution.
In the thirty-fourth aspect of the invention, the alkali-etched aluminum alloy plate is desmutted as in the 33rd aspect, by processing it in an acid solution having an acid concentration of from 250 to 500 g/liter and an aluminum ion concentration of from 1 to 15 g/liter, at 60 to 90xc2x0 C. for 1 to 180 seconds.
In the thirty-fifth aspect of the invention, the aluminum alloy plate is mechanically roughened on its surface, before it is processed in the alkali-etching step as in the 33rd aspect.
In the thirty-sixth aspect of the invention, the aluminum alloy plate is, after processed for anodic oxidation as in the 30th aspect, further processed for surface pore sealing and/or for surface hydrophilication.
In the thirty-seventh aspect of the invention, the surface of the aluminum alloy plate is activated before it is electrolytically roughened as in the 30th aspect.
The thirty-eighth aspect of the invention is the support for planographic printing plates produced according to the production method of any of the above-mentioned 30th to 38th aspects.
The thirty-ninth aspect of the invention is a planographic printing plate precursor, which is fabricated by forming an undercoat layer having a dry weight of from 0.001 to 1 g/m2, a positive or negative photosensitive layer having a dry weight of from 1 to 3 g/m2, and a mat layer having a dry weight of from 0.001 to 1 g/m2, in that order on the surface of the support of the 38th aspect as above.
In the fortieth aspect of the invention, the planographic printing plate precursor of the 39th aspect has a surface roughness (Ra) falling between 0.3 and 0.6 xcexcm, a value L* falling between 50 and 95, and a delta Eab* of at most 2.
The forty-first aspect of the invention is an aluminum plate for planographic printing plate supports, which has an aluminum content of from 95 to 99.4% by weight and is produced in a rolling process, and which, when measured in point of the number of the strains at its machine-direction (MD) edges and of the height of the strains according to a process comprising the following steps (a) to (d):
(a) cutting the aluminum plate in the direction nearly perpendicular to the machine direction thereof,
(b) putting the thus-cut aluminum piece on the flat or curved, sample-receiving face of a sample stand,
(c) pressing it against the sample-receiving face of the stand so that the center part of the aluminum piece around the center line thereof that runs in the machine direction is firmly stuck to the sample-receiving face of the stand throughout the overall length of the aluminum piece in the machine direction, and
(d) measuring the aluminum piece thus on the stand, in point of the number of the waved edge strains per the unit length of each edge and of the height of each edge strain, satisfies the conditions that the number of the MD edge strains thereof is at most 3.334 per meter of each edge, the maximum height of the edge strains is at most 2 mm, and the total height of all the edge strains is at most 2.666 mm.
For the aluminum plate, usable are those prepared by hot and/or cold rolling aluminum alloys that are produced by adding mother alloys and/or pure metal additives to virgin ingots such as those mentioned hereinabove, or those prepared by hot and/or cold rolling cast slabs of such virgin ingots. For it, however, preferred are aluminum plates prepared by hot and/or cold rolling cast slabs of recycled aluminum, scrapped aluminum and regenerated ingots such as those mentioned hereinabove, as well as aluminum plates prepared by hot and/or cold rolling cast slabs of such recycled aluminum, scrapped aluminum and regenerated ingots additionally containing scrapped aluminum of planographic printing plates.
The aluminum plate for planographic printing plate supports in this aspect is continuously processed for surface roughening, anodic oxidation, plate layer formation, cutting and slitting to fabricate planographic printing plate precursors, and the process is free from plate feed disorder such as plate meandering or entangling. In addition, when the planographic printing plate precursors thus prepared by processing the aluminum plate are further processed into printing plates, they do not meander or entangle in the processing units and in the developing units. Moreover, when the printing plate is set around the blanket in a planographic offset printer, it does not lift up from the surface of the blanket.
Another advantage of the aluminum plate for planographic printing plate supports is that the cost of its materials can be reduced since it can be produced from recycled aluminum, scrapped aluminum and regenerated ingots.
In the forty-second aspect of the invention, the aluminum plate for planographic printing plate supports of the 41st aspect is so profiled that its center part is thick and the area around its edges is thin, and its cross section is so controlled that the value a and the value pc defined by the following equations are at most 1% and at most 2%, respectively:
a=h/c, 
pc=c/tmax, 
wherein h=tminxe2x88x92tedge; c=tmaxxe2x88x92tmin; tmax=the maximum thickness of the center part of the aluminum web; tmin=the minimum thickness of the aluminum web; tedge=the thickness of the edges of the aluminum web.
The aluminum plate for planographic printing plate supports of this aspect is so controlled that its center part is thick and the area around its edges is thin. Therefore, when wound up in coils, its edges are prevented from being roughly contacted with each other to be deformed. In addition, it is so controlled that the thickness of the center part of the aluminum plate is not so large and the thickness of the area around the edges thereof is not so small, as compared with the mean thickness of the plate in the direction of the width thereof. Therefore, when wound up in coils, the aluminum plate is not unfavorably deformed.
In the forty-third aspect of the invention, the silicon content of the aluminum plate for planographic printing plate supports falls between 0.15 and 1% by weight.
In general, recycled aluminum, scrapped aluminum and regenerated ingots contain much silicon or much manganese. The aluminum plate for planographic printing plate supports of this aspect is one embodiment of aluminum plates prepared from those containing much silicon.
In the forty-fourth aspect of the invention, the manganese content of the aluminum plate for planographic printing plate supports falls between 0.1 and 1.5% by weight.
The aluminum plate for planographic printing plate supports of this aspect is one embodiment of aluminum plates prepared from recycled aluminum, scrapped aluminum and regenerated ingots containing much manganese.
In the forty-fifth aspect of the invention, the aluminum plate for planographic printing plate supports is so defined that the degree of its bending in the machine direction is at most 0.3 mm/4 m.
In the forty-sixth aspect of the invention, the aluminum plate for planographic printing plate supports is so defined that the height of the burrs at its edges is at most 10 xcexcm.
The forty-seventh aspect of the invention is a support for planographic printing plates, which is produced by roughening at least one surface of the aluminum plate for planographic printing plate supports of any one of the 41st to 46th aspects.
In the forty-eighth aspect of the invention, the aluminum plate for planographic printing plate supports, of which the surface has been roughened as in the 47th aspect, is subjected to anodic oxidation to thereby form an oxide film on its roughened surface.
The forty-ninth aspect of the invention is a method for inspecting aluminum plates for planographic printing plate supports, which comprises;
(a) a step of cutting a rolled aluminum plate in the direction nearly perpendicular to the machine direction thereof,
(b) a step of putting the thus-cut aluminum piece on the flat or curved, sample-receiving face of a sample stand,
(c) a step of pressing it against the sample-receiving face of the stand so that the center part of the aluminum piece around the center line thereof that runs in the machine direction is firmly stuck to the sample-receiving face of the stand throughout the overall length of the aluminum piece in the machine direction, and
(d) a step of measuring the aluminum piece thus on the stand, in point of the number of the waved edge strains per the unit length of each edge and of the height of each edge strain.
The rolled aluminum plate is generally wound up in coils in the machine direction thereof. Therefore, when its coils are uncoiled, the uncoiled plate is often still curved or curled in the machine direction as it is habituated to winding up in coils.
However, according to the method of this aspect for inspecting aluminum plates for planographic printing plate supports, the aluminum plate to be inspected is pressed against a sample stand in the overall length in the machine direction thereof as in the above, and the center part of the aluminum plate is kept firmly contacted with the sample-receiving face of the stand in the overall length of the aluminum plate. Therefore, the edge strains, if any, of the aluminum plate thus inspected will lift up from the sample-receiving face of the stand.
Specifically, according to the inspection method of this feature, uncoiled aluminum plates can be checked for the presence or absence of their edge strains while they are completely free from their habit to curl. Therefore, in the method, there should be no misunderstanding about the differentiation of the waved edge strains of uncoiled aluminum plates that are derived the habit of the uncoiled aluminum plates to curve, from the original edge strains that are intrinsic to the aluminum plates.
The sample stand usable in the inspection method may have a flat face to receive a sample thereon. For example, the sample stand of the type includes level tables made of cast matters such as cast iron, and glass level tables having a sample-receiving face of glass.
Apart from these, also usable herein are sample stands of which the sample-receiving face is columnar or curved. One example of the sample stands of the type is a blanket for planographic offset printers.
For pressing the aluminum plate against the sample-receiving face of the stand, for example, employable is a method of putting a weight that is longer than the overall length of the aluminum plate in the machine direction thereof, on the top face of the aluminum plate. This will be described hereinunder. Apart from the method, an operator may press the aluminum plate against the stand by hand.
The height of the edge strains of the aluminum plate may be measured, for example, by inserting a taper gauge into the space between the strained edge of the aluminum plate and the sample-receiving face of the sample stand on which it carries the aluminum plate, and reading the level of the taper gauge that indicates the height of the edge strain from the sample-receiving face of the stand, as will be described in the embodiments of the invention given hereinunder.
Apart from the method, also employable is a method of taking a picture of the aluminum plate that is on the sample-receiving face of the sample stand under pressure, by the use of an ordinary camera or a digital camera, and measuring the height of the edge strains of the aluminum plate on the picture.
In the fifties feature of the invention, the sample stand is a level table of which the sample-receiving face is flat.
The flat sample-receiving face of the level table is finished with high accuracy. Therefore, according to the inspection method of this feature, the edge strains of the aluminum plate inspected can be detected accurately.
In the fifty-first feature of the invention, one or more weights are put in the center part of the sample set on the sample-receiving face of the sample stand, covering the overall length of the sample in the machine direction thereof, and the sample is firmly pressed against the sample-receiving face of the stand by those weights.
According to the inspection method of this feature, the aluminum plate to be checked for the presence or absence of edge strains and for the height of edge strains, if any, can be surely pressed against the stand in the overall length in the machine direction thereof.
In the fifty-second feature of the invention, the sample to be inspected is set on the sample stand in such a manner that the outer side edge of the weight put on the sample is inside the adjacent side edge of the sample by 0.1 w to 0.3 w, with w indicating the width of the sample.
According to the inspection method of this feature, the center part of the aluminum plate can be surely firmly held on the sample-receiving face of the sample stand, and, when the aluminum plate has edge strains, its edge strains are prevented from being pressed against the sample stand and are therefore surely detected and measured.